Resolution is the process whereby a racemic modification, be it racemic mixture, racemic compound or racemic solution, is separated into its enantiomers. The most popular method consists in converting the enantiomers of a racemic modification into diastereoisomers which in turn are separated e.g., by fractional crystallization or chromatography. Thus, e.g. racemic acids may be separated by optically active bases, and racemic alcohols resolved by optically active acids or derivatives thereof.
Interphenylene-9-thia-11-oxo-12-azaprostanoic acids having pharmaceutical activity are described in U.S. Pat. No. 4,225,609. It has now been discovered that racemic mixtures of these acids can be resolved to provide individual enantiomers of the acids using camphanic acid or a camphorcarboxylic acid as the resolving agent. The resolution proceeds through formation of ester diastereomers, separation of the diastereomers and subsequent hydrolysis to obtain the corresponding enantiomeric acids.